The vertebrae in a patient's spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage that allow the joints to move or articulate relative to one another.
Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to restore function to the three joint complex. Damaged, diseased levels in the spine were traditionally fused to one another. While such a technique may relieve pain, it effectively prevents motion between at least two vertebrae. As a result, additional stress may be applied to the adjoining levels, thereby potentially leading to further damage.
More recently, techniques have been developed to restore normal function to the facet joints. One such technique involves covering the facet joint with a cap to preserve the bony and articular structure. Capping techniques, however, are limited in use as they will not remove the source of the pain in osteoarthritic joints. Caps are also disadvantageous as they must be available in a variety of sizes and shapes to accommodate the wide variability in the anatomical morphology of the facets. Caps also have a tendency to loosen over time, potentially resulting in additional damage to the joint and/or the bone support structure containing the cap.
Other techniques for restoring the normal function to the posterior element involve arch replacement, in which superior and inferior prosthetic arches are implanted to extend across the vertebra typically between the spinous process. These arches can articulate relative to one another to replace the articulating function of the facet joints. One drawback to current articulating facet replacement devices, however, is that they require the facet joints to be resected, which entails an invasive surgery. Moreover, alignment of the articulating surfaces with one another can be challenging.
Accordingly, there remains a need for improved systems and methods that are adapted to mimic the natural function of the facet joints.
Traditional spine fusion may result in early degeneration at adjacent spine levels due to increased loading and compensation. This may result in subsequent surgeries to fuse additional levels. Stabilization using more dynamic rods with traditional pedicle screw instrumentation may improve surgical outcomes and reduce additional surgeries for adjacent level degeneration.
U.S. Pat. No. 7,419,714 (Magerl) discloses a composite of polymer or ceramic material having reinforcing fibers. The composite is used to manufacture medical implants such as osteosynthesis plates, endoprostheses, screw coupling elements, surgical instruments, and similar components. The reinforcing fibers and fibrous parts are made from a material that absorbs X-rays so that it can be seen during X-ray examination. Magerl proposes that the composite comprises a polymer or ceramic material with a high fiber percentage, primarily using continuous, long or short fibers, wherein at least a small percentage of fibers or fibrous parts consist of a material with a high X-ray absorption. Despite a very high percentage of continuous fibers, the volume percentage of residual material can be retained, and the existing strength characteristics can be retained or even enhanced through the sole replacement of otherwise present fibers with fibers consisting of a material with a high X-ray absorption. In one embodiment, it is proposed that the composite consist of carbon fiber-reinforced PAEK (poly-aryl-ether-ketone) and a percentage of fibers made out of a material with a high X-ray absorption. This makes it a material with a special compatibility, high strength and the visibility necessary for X-ray diagnostics. Optimal strength levels can be achieved by designing the carbon fibers and fibers made out of a material with a higher X-ray absorption as continuous fibers and/or fibers with a length exceeding 3 mm. To enable a transfer of force between the fibers and the other material of the composite, i.e., to also ensure an optimal strength at a high volume density of fibers, the selected fibers should be enveloped on the surface by the matrix material both in the preform and in the finished component.